Glossy pilling-resistant acrylic fiber, method for producing same, and spun yarn and knitted fabric containing said acrylic fiber

ABSTRACT

The present invention provides: an acrylic fiber having a fineness of 0.5 to 3.5 dtex and having excellent gloss, pilling resistance, and texture; a method for producing said acrylic fiber; and a spun yarn and a knitted fabric containing said acrylic fiber. Provided is an acrylic fiber having a filament fineness of 0.5 to 3.5 dtex, wherein the product K of the value of knot strength (cN/dtex) and the value of knot elongation (%) is from 8 to 30 inclusive, and the number of recesses having a depth of 0.1 μm or greater is 10 or fewer.

TECHNICAL FIELD

The present invention relates to a pilling-resistant acrylic fiber thatexhibits excellent gloss and soft texture, to a method for producing theacrylic fiber, and to a spun yarn and a knitted fabric that contain theacrylic fiber.

BACKGROUND ART

Acrylic fibers have excellent characteristics such as soft texture, heatretention capability, shape stability, weather resistance anddyeability, and are widely used in apparel and interior applications thesame as other synthetic fibers such as nylon and polyester fibers.However, when fiber products made of acrylic fibers are in use, pillingtends to occur. Accordingly, the appearance and texture of knittedfabrics are significantly lowered and their commercial value is reduced.Therefore, technological development has been sought for a so-calledpilling-resistant acrylic fiber in which pilling rarely occurs.

Meanwhile, to achieve softer texture in apparel products, degrees offiber fineness have become even smaller recently, and development ofproducts using fibers with a smaller fiber fineness is in progress.Since pilling is more likely to occur when the degree of fiber finenessis smaller, demand for improved pilling-resistance properties is on therise.

In addition to improving the texture of apparel products, it has beenproposed to enhance gloss to express high quality similar to that ofsilk. For example, Patent Literature 1 (JP H11-222716A) proposes anacrylic fiber having a large single fiber fineness of 6˜34 dtex with aflat cross section, which is set to have enhanced gloss by formingsmooth portions of at least a certain size on the fiber surface. PatentLiterature 2 (JP2012-36512A) proposes a glossy acrylic fiber which isset to have a circular, or an elliptical but almost circular, fibercross section and to have a recessed curvature on the edge of the crosssection. Those fibers are each set to have a large single fiber finenessof 6 dtex or greater, while having a flat or broad-bean shapedcross-section.

Moreover, Patent Literature 3 (JP2006-176937A) and Patent Literature 4(JP2008-38309A) each propose a yarn containing a pilling-resistantacrylic fiber with a smaller fiber fineness along with its manufacturingmethod. However, none of such smaller-fineness acrylic fibers hasachieved both pilling-resistance and glossy properties.

Patent Literature 5 (JP2011-12363A) proposes a carbon-fiber-precursoracrylic fiber which is structured to have fewer irregularities on fibersurfaces and to have a single fiber fineness of 1.1 dtex. However, sincethe strength of the carbon-fiber-precursor acrylic fiber is enhanced,the knot strength and knot elongation are smaller. Accordingly, thecarbon-fiber-precursor acrylic fiber tends to break during the spinningprocess and thus is not suitable for forming yarn.

CITATION LIST Patent Literature

Patent Literature 1: JP H11-222716A

Patent Literature 2: JP2012-36512A

Patent Literature 3: JP2006-176937A

Patent Literature 4: JP2008-38309A

Patent Literature 5: JP2011-12363A

SUMMARY OF THE INVENTION Problems to be Solved by the Invention

Considering the above, the objective of the present invention is toprovide an acrylic fiber with a fiber fineness of 0.5˜3.5 dtex, which isset to exhibit excellent gloss and pilling resistance while having softtexture, and to provide its manufacturing method. The present inventionalso provides a spun yarn and knitted product containing such an acrylicfiber.

Solutions to the Problems

An acrylic fiber related to the present invention is set to have acenter-line mean roughness (Ra) of 3 nm to 12 nm on a single fibersurface, and a single fiber fineness of 0.5 dtex to 3.5 dtex.

The acrylic fiber related to the present invention is preferred to havea product (K) of 10 to 30 obtained by multiplying the value of knotstrength (cN/dtex) and the value of knot elongation (%).

The acrylic fiber related to the present invention is structured to havea center-line mean roughness (Ra) of 3 nm to 12 nm on a single fibersurface, and to have a product (K) of 10 to 30 obtained by multiplyingthe value of knot strength (cN/dtex) and the value of knot elongation(%).

The acrylic fiber related to the present invention is preferred to havea single fiber fineness of 0.5 dtex to 3.5 dtex.

On the surface of an acrylic fiber related to the present invention, itis preferred that a maximum height (Ry) of the profile be set at 40 nmto 150 nm, a 30-point mean roughness (Rz) at 20 nm to 80 nm, and adistance (S) at 800 nm to 1100 nm between peaks of convex portions.

Regarding the acrylic fiber related to the present invention, the numberof recesses of 0.1 μm or deeper that are present on the surface of asingle fiber is preferred to be no greater than 10 when counted in thecross section perpendicular to the fiber axis.

The acrylic fiber related to the present invention is preferred tocontain 92 mass % to 96.8 mass % of an acrylonitrile unit, 2 mass % to 6mass % of a vinyl monomer unit, and 0.2 mass % to 2.0 mass % of asulfonic acid group-containing vinyl monomer unit, and to have a singlefiber tensile strength of 1.8 cN/dtex to 3.0 cN/dtex, a single fiberknot strength of 1.0 cN/dtex to 1.8 cN/dtex, and a single fiber knotelongation of 8% to 12%.

A method for producing acrylic fiber related to the present inventionincludes the following steps: forming a spinning dope by dissolving inan organic solvent an acrylonitrile-based copolymer that contains 92mass % to 96.8 mass % of an acrylonitrile unit and 0.2 mass % to 2.0mass % of a sulfonic acid group-containing vinyl monomer unit; forming acoagulated fiber bundle by discharging the spinning dope in a 35° C. to50° C. coagulation bath through multiple discharge ports of a spinningnozzle at a jet-stretch ratio of 0.4 to 2.2 times; stretching thecoagulated fiber bundle in 80° C. to 98° C. hot water at a stretch ratioof 2 to 3.8 times; applying oil to the fiber bundle and dryingthereafter; stretching the fiber bundle by applying dry heat to have afiber temperature of 150° C. to 170° C. at a stretch ratio of 1.2 to 3times; and setting the value of a product (S) to be 4 to 6 when obtainedby multiplying the hot-water stretch ratio and the dry-heat stretchratio.

In the method for producing the acrylic fiber related to the presentinvention, it is preferred that the acrylonitrile-based copolymerfurther contain 2 mass % to 6 mass % of a vinyl monomer unit, thesolvent concentration of the coagulation bath be 40 mass % to 60 mass %,and a thermal relaxation process be conducted after hot-dry stretching.

In the method for producing an acrylic fiber related to the presentinvention, the thermal relaxation process is preferred to have anannealing temperature of 120° C. to 135° C. and a fiber relaxation ratioof 5% to 20%.

A spun yarn related to the present invention contains the acrylic fiberat 40 mass % or greater, and has a cotton count of 40 to 70.

The spun yarn is preferred to contain a cellulose-based fiber at 10 mass% to 40 mass %.

A knitted fabric related to the present invention contains the spun yarnat 40 mass % or greater, has a basis weight of 150 g/m² to 230 g/m², andthe pilling resistant property is rated at 4 or higher.

The knitted fabric related to the present invention is preferred toexhibit a heat-retention rate of 15% to 50%.

Effects of the Invention

According to the present invention, an acrylic fiber is provided to beused in inner apparel applications, especially in applications forundergarments. Using the acrylic fiber, such fiber products exhibit asoft texture while showing high-grade gloss and excellent pillingresistance.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a single fiber surface, showing acenter-line mean roughness (R);

FIG. 2 is a cross-sectional view of a single fiber surface, showing amaximum height (Ry) of the profile;

FIG. 3 is a cross-sectional view of a single fiber surface, showing a30-point mean roughness (Rz); and

FIG. 4 is a cross-sectional view of a single fiber surface, showing adistance (S) between peaks of convex portions.

DETAILED DESCRIPTION OF THE EMBODIMENTS <Polymer Composition of AcrylicFiber>

In the acrylic fiber related to the present invention, the copolymer ispreferred to be formed by copolymerizing 92 mass % to 96.8 mass % of anacrylonitrile unit. When the copolymerization ratio of an acrylonitrileunit is 92 mass % or greater, it is easier to obtain the fiber strengthrequired for forming apparel fibers.

From the above viewpoint, the ratio of an acrylonitrile unit in acopolymer is more preferred to be 95 mass % or greater.

In addition, when the copolymerization ratio of an acrylonitrile unit is96.8 mass % or lower, excellent dyeability, fiber strength andelongation are expected to be achieved.

In the copolymer, the ratio of a vinyl monomer unit copolymerizable withacrylonitrile is preferred to be set at 3.0 mass % to 6.0 mass %. Whenthe polymerization ratio of a vinyl monomer unit is set in such a range,sufficient physical characteristics and dyeability necessary for knittedproducts are achieved.

Moreover, the copolymerization ratio of a sulfonic acid group-containingvinyl monomer unit in the copolymer is preferred to be set at 0.2 mass %to 2.0 mass %. When the copolymerization ratio of the sulfonic acidgroup containing-vinyl monomer is 0.2 mass % or greater, excellentdyeability is expected to be achieved, and when the ratio is 2.0 mass %or lower, an increase in cost is suppressed.

Examples of vinyl monomers copolymerizable with acrylonitrile are methylacrylate, methyl methacrylate, esters of (meth)acrylic acids, vinylacetate, styrene, acrylamide, 2-hydroxyethyl methacrylate, glycidylmethacrylate and the like. Preferred examples of sulfonic acidgroup-containing vinyl monomers are allyl sulfonic acid,methallylsulfonic acid, styrene sulfonic acid, vinylsulfonic acid,isoprene sulfonic acid, 2-acrylamide-2-methylpropanesulfonic acid, theirmetal salts and amine salts, and so on. However, those listed above arenot the only option to be used in the embodiments of the presentinvention. To prepare acrylonitrile-based copolymers, suspensionpolymerization carried out in an aqueous medium is preferred.

<Single Fiber Fineness of Acrylic Fiber>

The single fiber fineness of acrylic fiber related to the presentinvention is preferred to be set at 0.5 dtex to 3.5 dtex. Generally, thefiner the fiber is, the lower the color sharpness is when dyed. However,the acrylic fiber related to the present invention exhibits colorsharpness even though its fineness is 1.2 dtex or lower. A single fiberfineness of 0.5 dtex or higher contributes to achieving the effects ofcolor sharpness, while a single fiber fineness of 3.5 dtex or lowermakes it easier to obtain a soft texture when the fiber is formed into aknitted fabric. Considering those viewpoints, the single fiber finenessis more preferred to be 0.7 dtex to 2.0 dtex, even more preferably 0.8dtex to 1.2 dtex.

<Product (K)>

The acrylic fiber related to the present invention is preferred to havea product (K) of 10 to 30 obtained by multiplying the value of knotstrength (cN/dtex) and the value of knot elongation (%). The value ofproduct (K) is used as an index of pilling resistance by people skilledin the art.

When the product (K) is 10 or greater, fly waste caused by finely brokensingle fibers is less likely to occur during a spinning process. Whenthe product (K) is 30 or lower, excellent pilling resistance isachieved.

From the above viewpoints, the product (K) is more preferred to be 12 to25, even more preferably 14 to 20.

<Center-line Mean Roughness (Ra) on Single Fiber Surface>

The acrylic fiber related to the present invention has fewer recesses onthe surface, resulting in excellent gloss. The center-line meanroughness (Ra) on a single fiber surface is 3 nm to 12 nm. An (Ra) of 3nm or greater is preferred since the fiber is unlikely to slip becauseof the friction generated between the roll and the fiber duringspinning. An (Ra) of 12 nm or less is preferred since it is easier toexpress gloss. From such viewpoints, the (Ra) is more preferred to be 4nm to 10 nm, even more preferably 5 nm to 9 nm.

<Maximum Height (Ry) of the Profile, 30-point Mean Roughness (Rz),Distance (S) between Peaks of Convex Portions>

Regarding the surface of a single acrylic fiber related to the presentinvention, it is preferred that a maximum height (Ry) of the profile beset at 40 nm to 150 nm, a 30-point mean roughness (Rz) at 20 nm to 80nm, and a distance (S) between peaks of convex portions at 800 nm to1100 nm.

An (Ry) of 40 nm or greater is preferred since friction is generatedbetween fibers to improve processability in a spinning process, while an(Ry) of 150 nm or less is preferred since regular reflection is expectedto occur. From such viewpoints, the (Ry) is more preferred to be 50 nmto 100 nm, even more preferably 55 nm to 90 nm.

An (Rz) of 20 nm or greater is preferred since processability duringspinning is better, and an (Rz) of 80 nm is preferable since the glossis enhanced. From such viewpoints, the (Rz) is more preferred to be 30nm to 65 nm, even more preferably 35 nm to 50 nm.

An (S) of 800 nm or greater is preferred in view of fiber spinnability,while an (S) of 1100 nm or less is preferred since irregularities arefewer on a fiber surface and random reflection is less likely to occur.From such viewpoints, the (S) is more preferred to be 900 nm to 1000 nm.

<Number of Recesses on Fiber Surface>

Furthermore, regarding the acrylic fiber related to the presentinvention, the number of recesses of 0.1 μm or deeper is preferred to be10 or fewer when counted on the cross section of a single fiber cut in adirection perpendicular to the fiber axis. When observed in a crosssection perpendicular to the fiber axis using a later-described method,the number of recesses of 0.1 μm or deeper is preferred to be no greaterthan 10 on a fiber surface, since gloss is enhanced. When recesses of0.1 μm or deeper are present on a fiber surface, light reflectsrandomly. Thus, when the number of recesses of 0.1 μm or deeper is 10 orfewer on the acrylic fiber surface related to the present invention,gloss is enhanced since random reflections are less likely to occur, anda decrease in gloss is suppressed. From such viewpoints, the number ofrecesses of 0.1 μm or deeper is more preferred to be 5 or fewer. Toreduce irregularities on a fiber surface, it is effective to lower thestretch ratio when the coagulated fiber is stretched by wet heat.

The tensile strength of a single acrylic fiber related to the presentinvention is preferred to be 1.8 cN/dtex or greater, more preferably 2.0cN/dtex or greater, considering processability during a spinning processor the like. The upper limit of the tensile strength is not particularlyspecified, and 3.0 cN/dtex is sufficient.

The knot strength of a single acrylic fiber related to the presentinvention is preferred to be 1.0 cN/dtex to 1.8 cN/dtex.

When the knot strength is 1.0 cN/dtex or greater, fly waste is lesslikely to occur during a spinning process and processability isexcellent. When the knot strength is 1.8 cN/dtex or less, pillingresistance is improved. From such viewpoints, the knot strength is morepreferred to be 1.2 cN/dtex to 1.6 cN/dtex, even more preferably 1.4cN/dtex to 1.5 cN/dtex.

To enhance pilling resistance, the knot elongation of a single acrylicfiber related to the present invention is preferred to be at least 8%but no greater than 20%, more preferably no greater than 15%.

<Method for Producing Acrylic Fiber>

The acrylic fiber related to the present invention is produced by wetspinning or dry wet spinning. Wet spinning is preferred in terms ofproductivity and cost performance.

<Composition of Copolymer>

In the method for producing acrylic fiber related to the presentinvention, it is preferred to use an acrylonitrile-based copolymer thatcontains 92 mass % to 96.8 mass % of an acrylonitrile unit, 2 mass % to6 mass % of a vinyl monomer unit and 0.2 mass % to 2.0 mass % of asulfonic acid group containing-vinyl monomer unit.

A spinning dope is formed by dissolving the acrylonitrile-basedcopolymer in an organic solvent.

The spinning dope is preferred to contain 15 mass % to 30 mass % of theacrylonitrile-based copolymer and 70 mass % to 85 mass % of an organicsolvent. The acrylonitrile-based copolymer is preferred to have aconcentration of 15 mass % to 30 mass % in the spinning dope. Such aconcentration is preferred to achieve excellent spinnability, since yarnbreakage is less likely to occur and productivity is high. The copolymerconcentration is more preferred to be 18% to 25% in view ofspinnability.

The solvent is required to be an organic solvent, for example,dimethylacetamide, dimethylformamide, dimethyl sulfoxide and the like.Among them, dimethylacetamide is preferred from the viewpoint ofproductivity in fiber manufacturing and balancing the color sharpnessand anti-pilling properties of the obtained pilling-resistant acrylicfiber.

A temperature of 40° C. or higher is preferred for dissolving theacrylonitrile-based copolymer in an organic solvent, since fewerundissolved components will remain, thus prolonging the life span of afilter medium in a filtration system such as a filter press whilepreventing a decrease in thread-forming properties. On the other hand, adissolving temperature of 95° C. or lower is preferred since thecopolymer is less likely to undergo color change.

The temperature of the spinning dope after the acrylonitrile-basedcopolymer is dissolved in an organic solvent is preferred to be 40° C.to 95° C. If the temperature is set at 40° C. to 95° C., an increase innozzle pressure due to low viscosity, gelation of the spinning dope orthe like is prevented, thus optimizing thread-forming properties andspinnability.

<Temperature of Coagulation Bath>

Next, a coagulated fiber bundle is formed by discharging the spinningdope through multiple discharge ports of a spinning nozzle into acoagulation bath set to have a solvent concentration of 40 mass % to 60mass % and a temperature of 35° C. to 50° C.

When the solvent concentration and temperature are set in the aboveranges, coagulation at an undesired faster speed is prevented andrecessed wrinkles are less likely to be formed on a fiber surface.

<Jet-Stretch Ratio, Hot-water Stretch Ratio, Dry-heat Stretch Ratio,Multiplication Product of Stretch Ratios>

The jet-stretch ratio is preferred to be 0.4 to 2.2 when the spinningdope is discharged through spinning nozzle ports. The jet-stretch ratiois obtained when the draw velocity of coagulated fiber is divided by theextrusion velocity.

A jet-stretch ratio of 0.4 to 2.2 is preferred since fiber breakage isless likely to occur in the spinning bath and spinnability is therebyexcellent. From such viewpoints, the jet-stretch ratio is more preferredto be 0.6 to 2.0.

Moreover, the coagulated fiber bundle is stretched in hot water to havea stretch ratio of 2 to 4 times, and an oil agent is applied and driedon the fiber bundle. Then, the fiber bundle is stretched by applying dryheat to have a stretch ratio of 1.2 to 3 times. During those procedures,the value of a product (S), obtained by multiplying the hot-waterstretch ratio and the dry-heat stretch ratio, is set to be 4 to 6.

A dry-heat stretch ratio of at least 1.2 times is preferred, sincerecesses on a fiber surface are elongated to increase the area of smoothsurface, thus enhancing the gloss of the fiber. A dry-heat stretch ratioof no greater than 3 times is preferred, since pilling resistance isimproved and fiber breakage is reduced during a spinning process.

To reduce recesses on a fiber surface and to enhance gloss, the dry-heatstretch ratio is more preferred to be at least 1.5 times, even morepreferably at least 1.7 times. To improve processability, the stretchratio is preferred to be no greater than 2 times.

In addition, the product (S) is preferred to be 4 to 6, sinceprocessability during spinning is excellent, and appropriate fiberstrength is achieved. Also, pilling resistance is expected to beexcellent. The product (S) is more preferred to be 4.5 to 5.5.

<Temperature of Hot Water, Fiber Temperature for Dry-heat Stretching>

When the fiber is stretched in hot water, the water temperature ispreferred to be 80° C. to 98° C. In such a temperature range, fiberbreakage is less likely to occur during hot-water stretching.

In addition, the fiber temperature at the time for stretching by dryheat is preferred to be 150° C. to 170° C. A temperature of at least150° C. makes it easier to stretch wrinkles on the fiber surface, and atemperature of no higher than 170° C. reduces color change caused byheat while decreasing fiber breakage during dry-heat stretching.

Applying heat on a fiber bundle for dry-heat stretching may be conductedby using a hot roll, contact heating on a hot plate, or non-contactheating by hot air. Among them, hot roll heating is preferred becauseheat is efficiently applied on a fiber bundle.

By using a hot roll to apply heat on a fiber bundle, the fibertemperature is appropriately increased by adjusting the temperature ofthe hot roll and the time for the fiber bundle to be in contact with thehot roll. It is preferred to use multiple hot rolls so that bothsurfaces of the fiber bundle are heated.

The temperature of a hot roll is preferred to be 150° C. to 190° C. Atemperature of 190° C. or lower suppresses the color change of the fibercaused by heat.

Then, the dry-heat stretched fiber bundle is crimped and stored in acontainer.

The swelling degree of fiber that is stretched in hot water is preferredto be set at 80% to 130% A swelling degree of 80% to 130% is preferredsince dryness and productivity of the fiber are excellent. In addition,fewer wrinkles are expected to appear on the fiber surface.

<Thermal Relaxation>

Lastly, thermal relaxation is conducted on the fiber to have a thermalshrinkage rate of 5% to 20% to obtain the final product of acrylicfiber. Conditions for thermal relaxation are determined based on thethermal shrinkage rate of fiber. A fiber thermal shrinkage rate of 5% to20% is preferred since knot strength and knot elongation are set to havea value that is sufficient for exhibiting pilling resistance.

The thermal shrinkage rate means the rate of fiber shrinkage determinedwhen the fiber is compared before and after thermal relaxationtreatment.

The temperature for thermal relaxation is set at 120° C. to 135° C. Atemperature of 120° C. or higher is preferred since the strength andelongation of a single fiber are set to achieve excellent cardingprocessability during spinning, and a temperature of 135° C. or lowermakes it easier to obtain excellent pilling-resistant single fibers.

An acrylic fiber bundle produced by the above-described method is cutinto short fibers. The acrylic fiber was cut by a cutter to form shortfibers and then spun. Spun yarn may be formed with 100% of acrylic fiberrelated to the present invention, or may be formed by blending otherfibers, for example, synthetic or chemical fibers such as genericacrylic fibers, polyester fibers, nylon fibers and rayon fibers and/ornatural fibers such as cotton, wool and silk.

<Fiber Content of Spun Yarn>

The spun yarn related to the present invention is preferred to containthe aforementioned acrylic fiber at 40 mass % or greater. A content of40 mass % or greater contributes to expressing gloss and pillingresistance characterized in the acrylic fiber related to the presentinvention. From such viewpoints, the content is more preferred to be 60mass % or greater, even more preferably 80 mass % or greater.

<Yarn Count of Spun Yarn>

The yarn count of the spun yarn related to the present invention ispreferred to be a cotton count of 40 to 70. A cotton count of 40 orhigher makes it easier to form soft fabrics based on the effects derivedfrom a smaller fiber fineness of the acrylic fiber related to thepresent invention. In addition, a cotton count of 70 or lower makes iteasier to provide the strength required for the spun yarn during itsuse.

The coefficient of variation (CV) of yarn unevenness in the spun yarn ispreferred to be 11.5% or lower. When a CV is 11.5% or lower, a knittedfabric has good appearance with enhanced gloss. The CV is more preferredto be 11% or lower, even more preferably 10% or lower.

<Blending Ratio of Cellulose Fiber>

The spun yarn related to the present invention is preferred to contain acellulose fiber at 10 mass % to 40 mass %. A content of cellulose fiberat 10 mass % or greater enhances moisture-absorption and heat-generationproperties of the spun yarn. A content of 40 mass % or lower improvesthe pilling resistance and heat retention rate.

<Yarn Content of Knitted Fabric>

The knitted fabric related to the present invention is preferred tocontain the spun yarn at 40 mass % or greater. A content of 40 mass % orgreater contributes to achieving the effects of enhancing the gloss andpilling resistance of the knitted fabric. From such viewpoints, thecontent is more preferred to be 50 mass % or greater, even morepreferably 60 mass % or greater.

<Basis Weight of Knitted Fabric>

The knitted fabric related to the present invention is preferred to havea basis weight of 150 g/m² to 230 g/m². A basis weight of 150 g/m² orgreater increases the strength, and the knitted fabric is less likely tobe torn. A basis weight of 230 g/m² or less contributes to obtaining alightweight, soft, knitted fabric suitable for undergarments.

<Pilling Resistance>

The knitted fabric related to the present invention is preferred toexhibit a pilling resistance rated at 4 or higher. A pilling resistancerated at 4 or higher reduces the amount of pilling so as to give thefabric a clean appearance. The pilling resistance rating is morepreferred to be 4.5 or higher.

<Heat Retention>

The knitted fabric related to the present invention is preferred to havea heat retention rate of 15% to 50%. When the knitted fabric is madeinto undergarments, a heat retention rate of 15% or higher provideswarmth, and a heat retention rate of 50% or lower prevents excessivewarmth.

EXAMPLES

The acrylic fiber related to the present invention is described byreferring to the examples below.

(Method for Measuring Irregularities on Fiber Surface)

The depths of irregularities on the surface of an acrylic fiber relatedto the present invention are determined by the center-line meanroughness (Ra), maximum height (Ry) of the profile, 30-point meanroughness (Rz), and distance (S) between peaks, which are describedbelow. They are measured by using a laser microscope.

FIGS. 1˜4 are schematic views, each showing the surface of a singleacrylic fiber related to the present invention observed in a crosssection perpendicular to a fiber longitudinal direction.

(Center-Line Mean Roughness <Ra> on Single Fiber Surface)

As shown in FIG. 1, the center-line mean roughness (Ra) on the surfaceof a single fiber is the value expressed in nanometers (nm), which isdetermined in base length (L) taken out of the roughness curve to beparallel to the center line (m) when the distances from the center line(m) to the roughness-curve line are measured and the absolute deviationvalues are totaled to obtain the mean absolute deviation.

(Maximum Height <Ry> of the Profile of Single Fiber Surface)

As shown in FIG. 2, the maximum height (Ry) of the profile of a singlefiber surface is the value expressed in nanometers (nm), which isdetermined in base length (L) taken out of the roughness curve to beparallel to the center line (m) when the distance (Rp) from the highestpeak line to the center line (m) and the distance (Rv) from the lowestvalley line to the center line (m) are measured and the sum (Rp+Rv) isobtained.

(30-Point Mean Roughness <Rz> on Single Fiber Surface)

As shown in FIG. 3, the 30-point mean roughness (Rz) on the surface of asingle fiber is the value expressed in nanometers (nm), which isdetermined in the base length taken out of the roughness curve to beparallel to the center line when the mean absolute value of elevations(Yp) from the highest peak to the 15th highest peak and the meanabsolute value of elevations (Yv) from the lowest valley to the 15thlowest valley, both measured in a vertical direction of the profile, andthe sum (Yp+Yv) is obtained.

(Distance <S> between Peaks on Single Fiber Surface)

As shown in FIG. 4, the distance (S) between peaks on the surface of asingle fiber is the value expressed in nanometers (nm), which isdetermined in base length (L) taken out of the roughness curve to beparallel to the center line when the lengths corresponding to thedistances between adjacent peaks are measured and the mean distancevalue of multiple lengths between peaks of the convex portions isobtained.

(Tensile Strength and Elongation, Knot Strength and Knot Elongation)

Measurement was conducted in accordance with JIS L1015.

(Number of Recesses of 0.1 μm or Deeper on Single Fiber Surface)

After hot air was applied from a dryer on 200 to 300 acrylic fibersrelated to the present invention to stretch the shrunk fibers, thefibers were put into a tube. The tube was made of polyethylene thatshrinks only in a circumferential direction.

Next, the polyethylene tube filled with the acrylic fibers related tothe present invention was cut into approximately 2 mm lengths using anew razor blade in an approximate perpendicular direction to the axis.

One of the cut surfaces was fixed on a stage using a double-sided tape,and gold was deposited on the other cut surface set for observationusing a low-temperature ion sputtering apparatus (JFC1100, made by JEOLLtd.) under conditions of 1200 V and 5 mA for 8 minutes. Accordingly, anobservation sample of acrylic fibers related to the present inventionwas prepared.

Using a scanning electron microscope (model number XL-20, made byPhilips Electronics Company), a fiber cross section of the sample wascaptured at a magnification of 5000 times. The depth of a recess wasdetermined as the length of a line, which starts at the tangent lineconnecting convex portions on both sides of the recess and is drawnvertically down to the deepest spot of the recess. Then, the number ofrecesses of 0.1 μm or deeper was counted on the fiber surface. The sameprocedure was conducted on three samples, and the average value was setas the number of recesses of 0.1 μm or deeper present on a fiber crosssection.

(Evaluation of Gloss)

The gloss was evaluated as follows.

Acrylic fibers of Examples 1 and 2 and Comparative Example 1 were used100% to form spun yarns respectively under the same conditions, whichwere then formed into fabrics under the same conditions. The gloss ofeach fabric was visually evaluated.

∘: excellent gloss

×: poor gloss

Example 1

An acrylonitrile-based copolymer with a reduced viscosity of 1.8containing 95% of acrylonitrile, 4.4% of vinyl acetate and 0.6% ofsodium methallylsulfonate was dissolved in dimethylacetamide.Accordingly, a spinning dope was obtained, having a copolymerconcentration of 24% and a viscosity at 50° C. of 200 poise.

The spinning dope was discharged in a 41° C. coagulation bath with adimethylacetamide concentration of 56% through multiple discharge portswith a port diameter of 0.045 mm. Then, the obtained fiber was stretchedto be 2.5 times in 98° C. hot water while the solvent was washed out. Anoil agent was applied on the fibers and dried using multiple hot rollersset to have a surface temperature of 150° C. The fibers were furtherheated to 160° C. by applying heat using a 180° C. hot roller. Thefibers were stretched in air to be twice as long, crimped and put into acontainer.

Furthermore, thermal relaxation treatment was conducted on the fiberbundle to have a thermal shrinkage rate of 7% to 9%. Accordingly,acrylic fiber with a single fiber fineness of 1.0 dtex was prepared.Conditions are specified in Table 1 and results are shown in Table 2.

The product (K), obtained by multiplying knot strength (cN/dtex) andknot elongation (%) was 15.9, sufficient for exhibiting excellentpilling resistance. The number of recesses of 0.1 μm or deeper was two,and excellent gloss was obtained relative to comparative examples.

Example 2

The same spinning process as in Example 1 was conducted except that thewet-heat stretch ratio and the dry-heat stretch ratio were changed. Theconditions are specified in Table 1 and results are shown in Table 2.

Accordingly, the product (K) obtained by multiplying knot strength(cN/dtex) and knot elongation (%) was 16.6, sufficient for exhibitingexcellent pilling resistance. The number of recesses of 0.1 μm or deeperwas four, and excellent gloss was obtained relative to comparativeexamples.

Examples 3˜11

Acrylic fibers were prepared by conducting the same process as inExample 1 except that conditions for forming acrylic fibers were changedas respectively specified in Table 1. Physical properties of eachacrylic fiber are shown in Table 1.

Comparative Example 1

Acrylic fiber was prepared the same as in Example 1 except that nodry-heat stretching was conducted but the hot-water stretch ratio wasincreased to set the overall stretch ratio to be the same. Theconditions are specified in Table 1 and results are shown in Table 2.

Accordingly, the product (K) obtained by multiplying knot strength(cN/dtex) and knot elongation (%) was 25.7, at which pilling resistancewas exhibited, but the rating was not so high as that in the acrylicfiber related to the present invention. In addition, the number recessesof 0.1 μm or deeper was 15, and gloss was poor.

Comparative Example 2

Acrylic fiber was prepared the same as in Example 3 except that nodry-heat stretching was conducted but the hot-water stretch ratio wasincreased to set the overall stretch ratio to be the same. Theconditions are specified in Table 1 and results are shown in Table 2.

Accordingly, the product (K) obtained by multiplying knot strength(cN/dtex) and knot elongation (%) was 20, at which pilling resistancewas exhibited, but the rating was not so high as that in the acrylicfiber related to the present invention. In addition, gloss was poor.

Comparative Example 3

Acrylic fiber was prepared by the conditions described in JP2013-209771Afor producing a carbon-fiber-precursor acrylic fiber. The conditions arespecified in Table 1 and results are shown in Table 2.

The carbon-fiber-precursor acrylic fiber had a low value of product (K)obtained by multiplying knot strength and knot elongation. During thespinning process the fiber broke, indicating that the physicalproperties of the acrylic fiber were so low that the fiber could not bespun.

Comparative Example 4

According to the conditions described in JP H11-222716A for producingglossy fibers, acrylic fiber was prepared to have a single fiberfineness of 22 dtex and a flatness rate of 22. The conditions arespecified in Table 1 and results are shown in Table 2.

Accordingly, the product (K) was at a value sufficient for exhibitingpilling resistance, but the fiber fineness level was too high forachieving soft texture. Thus, the fiber is not suitable for apparelproducts.

TABLE 1 Spinning Coagulation Hot-water Dry-heat Thermal Single dopeCoagulation bath stretch stretch relaxation fiber Tensile AN/AV/MS temp.bath temp. concentration ratio ratio temp. fineness strength (mass %) (°C.) (° C.) (mass %) (times) (times) (° C.) (dtex) (cN/dtex) Example 195/4.4/0.6 75 41 56 2.5 2 128 1.0 2.6 Example 2 95/4.4/0.6 75 41 56 3.31.5 128 1.0 3 Example 3 95/4.4/0.6 80 45 56 2.25 2 123 0.8 2.69 Example4 95/4.4/0.6 80 45 56 2.25 2 128 0.8 2.55 Example 5 95/4.4/0.6 80 45 562.25 2 132 0.8 2.7 Example 6 95/4.4/0.6 80 45 56 2.65 1.7 123 0.8 2.78Example 7 95/4.4/0.6 80 45 56 2.65 1.7 128 0.8 2.55 Example 8 95/4.4/0.680 45 56 2.65 1.7 132 0.8 2.48 Example 9 95/4.4/0.6 80 35 56 2.25 2 1230.8 2.42 Example 10 95/4.4/0.6 75 45 56 2.25 2 123 0.8 2.46 Example 1195/4.4/0.6 80 41 56 3 1.5 132 0.8 3.17 Comp. 95/4.4/0.6 75 41 56 5 — 1281.0 2.8 Example 1 Comp. 95/4.4/0.6 80 45 56 4.5 — 123 0.8 2.77 Example 2Comp. AN/AAm/MA = 70 38 65 5.4 1.4 — 1.2 8.00 Example 3 96.5/5.7/0.8Comp. AN/AV = 93/7 85 30 30 2 2 140 22.0 1.63 Example 4 Center-line30-point Maximum Distance Number of Knot Knot Product (K) mean meanheight of (S) betw. recesses strength elongation (knot strength ×roughness roughness profile peaks of 0.1 μm (cN/dtex) (%) knotelongation) (Ra) (nm) (Rz) (nm) (Ry) (nm) (nm) or deeper Gloss Example 11.42 11.2 15.9 2 ∘ Example 2 1.44 11.5 16.6 5.7 38 64 940 4 ∘ Example 31.69 11.5 19.4 8.4 46 80 988 ∘ Example 4 1.42 12.1 17.2 ∘ Example 5 1.4813.9 20.6 ∘ Example 6 1.4 13.4 18.8 8.7 57 99 988 ∘ Example 7 1.25 10.613.3 ∘ Example 8 1.28 13.7 17.5 ∘ Example 9 1.59 17.3 27.5 9.5 56 98 988∘ Example 10 1.51 15.4 23.3 10 63 103 ∘ Example 11 1.62 9.5 15.9 9 50 92∘ Comp. 1.76 16.7 29.4 14.6 105 194 984 15 x Example 1 Comp. 1.35 14.820 15.6 93 185 15 x Example 2 Comp. 1.19 1.4 1.7 80 460 720 13 x Example3 Comp. 1.31 14.1 18.5 6.3 40 70 4 ∘ Example 4

Example 12

By blending 70 mass % of the acrylic fiber prepared in Example 1 and 30mass % of MicroModal (1.0 dtex, made by Lenzing Corporation), a spunyarn was formed to have a cotton count of 50 and a twist count of 873t/m. Its physical properties are shown in Table 2.

Example 13

Using 100% of the acrylic fiber prepared in Example 1, a spun yarn wasformed to have a cotton count of 60 and a twist count of 1139 t/m. Itsphysical properties are shown in Table 2.

Examples 14, 15

Spun yarns were obtained the same as in Example 13 except that theircotton counts were changed respectively as specified in Table 2. Theirphysical properties are shown in Table 2.

Example 16

A spun yarn was formed by using 100 mass % of the acrylic fiber preparedin Example 11. The cotton count was 40 and the twist count 820 t/m.Their physical properties are shown in Table 2.

Comparative Example 5

By blending 70 mass % of the acrylic fiber prepared in ComparativeExample 1 and 30 mass % of MicroModal (1.0 dtex, made by LenzingCorporation), a spun yarn was formed to have a cotton count of 50 and atwist count of 900 t/m. Its physical properties are shown in Table 2.

When compared with the fiber in Example 12, the variations in yarnunevenness were greater.

When spun yarns prepared in Example 12 and Comparative Example 5, eachwound on a cone, were visually compared, it was verified that the spunyarn of Example 12 had better gloss.

Using 100 mass % of the acrylic fiber prepared in Comparative Example 1,a spun yarn was formed to have a cotton count of 60 and a twist count of1139 t/m. Its physical properties are shown in Table 2.

Variations in yarn unevenness were greater than those in the spun yarnof Example 13.

Comparative Examples 7, 8

A spun yarn was formed the same as in Comparative Example 6 except thatthe cotton count was changed as specified in Table 2. Its physicalproperties are shown in Table 2.

Comparative Example 9

Using 100 mass % of the acrylic fiber of Comparative Example 2, a spunyarn was formed to have a cotton count of 40 and a twist count of 820t/m. Its physical properties are shown in Table 2.

When spun yarns prepared in Examples 13˜16 and Comparative Examples 6˜9,each wound on a cone, were visually compared, it was verified that spunyarns of the examples had better gloss than those of the comparativeexamples.

Example 17

Using the spun yarn of Example 15, a jersey weft-knit fabric wasprepared by setting the gauge at 14G. The basis weight was 210 g/m², theanti-pilling rating was 4.5, and the heat retention rate was 45.1%.

Comparative Example 10

Using the spun yarn of Comparative Example 8, a jersey weft-knit fabricwas prepared by setting the gauge at 14G. The basis weight was 210 g/m²,the anti-pilling rating was 4.5, and the heat retention rate was 44.9%.

However, the gloss was not as good as that of Example 17.

TABLE 2 Twist Strength of CV of CV of yarn Blend ratio Cotton countsingle yarn strength Elongation unevenness Yarn structure (mass %) count(t/m) (g) (%) (%) (%) Example 12 acrylic fiber of 70 50 873 7.01 12.989.56 Examp. 1 MicroModal 30 Example 13 acrylic fiber of Examp. 1 100 601139 9.49 14.37 12.22 Example 14 acrylic fiber of Examp. 1 100 50 10388.73 15.4 11.16 Example 15 acrylic fiber of Examp. 1 100 40 921 9.7216.76 9.82 Example 16 acrylic fiber of Examp. 11 100 40 820 210.6 11.116.8 11.7 Comp. acrylic fiber of Comp. 70 40 921 14.6 14.3 Example 5Examp. 1 MicroModal 30 Comp. acrylic fiber of Comp. 100 60 1100 118 9 1314.3 Example 6 Examp. 1 Comp. acrylic fiber of Comp 100 50 1000 178 11.314 14 Example 7 Examp 1 Comp. acrylic fiber of Comp. 100 40 890 229 10.116 13.8 Example 8 Examp. 1 Comp. acrylic fiber of Comp. 100 40 820 227.210.1 16.9 11.9 Example 9 Examp. 2

TABLE 3 Basis Pilling Heat weight resistance retention rate Spun yarn(g/m²) (rating) (%) Example 17 Example 15 210 4.5 45.1 Comp. Comp. 2104.5 44.9 Example 10 Example 8

1. An acrylic fiber, configured to have a center-line mean roughness(Ra) of 3 nm to 12 nm on the surface of a single fiber, and a singlefiber fineness of 0.5 dtex to 3.5 dtex.
 2. An acrylic fiber, configuredto have a center-line mean roughness (Ra) of 3 nm to 12 nm on thesurface of a single fiber, and a product (K) of 10 to 30 obtained bymultiplying the value of knot strength (cN/dtex) and the value of knotelongation (%).
 3. The acrylic fiber according to claim 1, wherein thevalue of a product (K), obtained by multiplying the value of knotstrength (cN/dtex) and the value of knot elongation (%), is set to be 10to
 30. 4. The acrylic fiber according to claim 2, wherein a single fiberfineness is set at 0.5 dtex to 3.5 dtex.
 5. The acrylic fiber accordingto claim 1, wherein the surface of a single fiber is configured to havea maximum height (Ry) of the profile set at 40 nm to 150 nm, the30-point mean roughness (Rz) at 20 nm to 80 nm and the distance (S)between peaks of convex portions at 800 nm to 1100 nm.
 6. The acrylicfiber according to claim 1, wherein the number of recesses of 0.1 μm ordeeper that are present on the surface of a single fiber is no greaterthan 10 when observed in a cross section perpendicular to the fiberaxis.
 7. The acrylic fiber according to claim 1, comprising 92 mass % to96.8 mass % of an acrylonitrile unit, 2 mass % to 6 mass % of a vinylmonomer unit, and 0.2 mass % to 2.0 mass % of a sulfonic acidgroup-containing vinyl monomer unit, wherein a single fiber tensilestrength is set at 1.8 cN/dtex to 3.0 cN/dtex, a single fiber knotstrength is set at 1.0 cN/dtex to 1.8 cN/dtex, and a single fiber knotelongation is set at 8% to 20%.
 8. A method for producing an acrylicfiber, comprising: forming a spinning dope by dissolving in an organicsolvent an acrylonitrile-based copolymer that contains 92 mass % to 96.8mass % of an acrylonitrile unit and 0.2 mass % to 2.0 mass % of asulfonic acid group containing-vinyl monomer unit; forming a coagulatedfiber bundle by discharging the spinning dope in a 35° C. to 50° C.coagulation bath through the discharge ports of a spinning nozzle at ajet-stretch ratio of 0.4 to 2.2; stretching the coagulated fiber bundlein 80° C. to 98 C.° hot water at a stretch ratio of 2 to 3.8 times;applying oil to the fiber bundle and drying the fiber bundle; andstretching the fiber bundle by applying dry heat to have a fibertemperature of 150° C. to 170° C. at a stretch ratio of 1.2 to 3 times,wherein the value of a product (S), obtained by multiplying thehot-water stretch ratio and the dry-heat stretch ratio, is set to be 4to
 6. 9. The method for producing an acrylic fiber according to claim 8,wherein the acrylonitrile-based copolymer is configured to furthercomprise 2 mass % to 6 mass % of a vinyl monomer unit, the solventconcentration of the coagulation bath is set to be 40 mass % to 60 mass%, and a thermal relaxation process is conducted after hot-drystretching.
 10. The method for producing an acrylic fiber according toclaim 8, wherein the temperature for the thermal relaxation process isset at 120° C. to 135° C., and a fiber relaxation ratio is set at 5% to20%.
 11. A spun yarn, comprising: an acrylic fiber according to claim 1at 40 mass % or greater, wherein the cotton count is set at 40 to 70.12. The spun yarn according to claim 11, further comprising acellulose-based fiber at 10 mass % to 40 mass %.
 13. A knitted fabric,comprising: a spun yarn according to claim 11 at 40 mass % or greater,wherein the basis weight is set at 150 g/m² to 230 g/m², and thepilling-resistant property is rated at 4 or higher.
 14. The knittedfabric according to claim 13, wherein a heat-retention rate is set to be15% to 50%.
 15. The acrylic fiber according to claim 2, wherein thesurface of a single fiber is configured to have a maximum height (Ry) ofthe profile set at 40 nm to 150 nm, the 30-point mean roughness (Rz) at20 nm to 80 nm and the distance (S) between peaks of convex portions at800 nm to 1100 nm.
 16. The acrylic fiber according to claim 2, whereinthe number of recesses of 0.1 μm or deeper that are present on thesurface of a single fiber is no greater than 10 when observed in a crosssection perpendicular to the fiber axis.
 17. The acrylic fiber accordingto claim 2, comprising 92 mass % to 96.8 mass % of an acrylonitrileunit, 2 mass % to 6 mass % of a vinyl monomer unit, and 0.2 mass % to2.0 mass % of a sulfonic acid group-containing vinyl monomer unit,wherein a single fiber tensile strength is set at 1.8 cN/dtex to 3.0cN/dtex, a single fiber knot strength is set at 1.0 cN/dtex to 1.8cN/dtex, and a single fiber knot elongation is set at 8% to 20%.
 18. Aspun yarn, comprising: an acrylic fiber according to claim 2 at 40 mass% or greater, wherein the cotton count is set at 40 to
 70. 19. The spunyarn according to claim 18, further comprising a cellulose-based fiberat 10 mass % to 40 mass %.
 20. A knitted fabric, comprising: a spun yarnaccording to claim 18 at 40 mass % or greater, wherein the basis weightis set at 150 g/m² to 230 g/m², and the pilling-resistant property israted at 4 or higher